WARNING: This page is about a different car, the 2004 Buick Regal and 2004 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Dome Lamp Lens
Courtesy of GENERAL MOTORS CORP.
Install the bulb to the dome lamp socket.
Align the dome lamp lens housing to the base plate and press into place until fully seated.